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timekeeping: Always check for negative motion

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clocksource_delta() has two variants. One with a check for negative motion,
which is only selected by x86. This is a historic leftover as this function
was previously used in the time getter hot paths.

Since 135225a363 timekeeping_cycles_to_ns() has unconditional protection
against this as a by-product of the protection against 64bit math overflow.

clocksource_delta() is only used in the clocksource watchdog and in
timekeeping_advance(). The extra conditional there is not hurting anyone.

Remove the config option and unconditionally prevent negative motion of the
readout.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241031120328.599430157@linutronix.de
This commit is contained in:
Thomas Gleixner 2024-10-31 13:04:08 +01:00
parent d44d26987b
commit c163e40af9
3 changed files with 0 additions and 13 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
arch/x86/Kconfig
View file

@ -145,7 +145,6 @@ config X86
select ARCH_HAS_PARANOID_L1D_FLUSH
select BUILDTIME_TABLE_SORT
select CLKEVT_I8253
select CLOCKSOURCE_VALIDATE_LAST_CYCLE
select CLOCKSOURCE_WATCHDOG
# Word-size accesses may read uninitialized data past the trailing \0
# in strings and cause false KMSAN reports.

5
kernel/time/Kconfig
View file

@ -17,11 +17,6 @@ config ARCH_CLOCKSOURCE_DATA
config ARCH_CLOCKSOURCE_INIT
bool
# Clocksources require validation of the clocksource against the last
# cycle update - x86/TSC misfeature
config CLOCKSOURCE_VALIDATE_LAST_CYCLE
bool
# Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL
bool

7
kernel/time/timekeeping_internal.h
View file

@ -30,7 +30,6 @@ static inline void timekeeping_inc_mg_floor_swaps(void)
#endif
#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
{
u64 ret = (now - last) & mask;
@ -41,12 +40,6 @@ static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
*/
return ret & ~(mask >> 1) ? 0 : ret;
}
#else
static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
{
return (now - last) & mask;
}
#endif
/* Semi public for serialization of non timekeeper VDSO updates. */
unsigned long timekeeper_lock_irqsave(void);